1. Technical Field
The present invention relates to a ferroelectric memory element including a memory cell array and a method for manufacturing the same.
2. Related Art
In a process for manufacturing a ferroelectric memory element, after a ferroelectric capacitor is formed, a ferroelectric layer may be exposed to a hydrogen atmosphere at the time of forming an interlayer insulation layer and conducting dry etching. A ferroelectric layer is generally composed of a metal oxide. For this reason, when the ferroelectric layer is exposed to hydrogen, oxygen contained in the ferroelectric layer is reduced by the hydrogen. As a result, the ferroelectric layer is damaged. For example, when a ferroelectric layer consists of SBT (SrBi2Ta2O9), and the SBT is reduced by hydrogen, the metal Bi is generated at grain boundaries, and the upper electrode and the lower electrode would become short-circuited. To prevent the deterioration by reduction of the ferroelectric layer, a so-called hydrogen barrier film that is a protection film is formed around the ferroelectric capacitor.
However, with the conventional memory element structure, it is extremely difficult to completely cover the ferroelectric layer with a hydrogen barrier film. For example, Japanese laid-open patent application 2000-68987 describes a hydrogen barrier film formed on a ferroelectric capacitor. However, contact holes are formed in the hydrogen barrier film over the upper electrodes for connecting the upper electrodes to a peripheral circuit section. Also, contact holes are formed in the hydrogen barrier film below the lower electrodes for connecting the lower electrodes to the peripheral circuit section. There is therefore a problem in that hydrogen can readily enter the contact hole sections where the hydrogen barrier film is not formed, and the ferroelectric layer is reduced.
It is an object of the present invention to provide a ferroelectric memory element in which its ferroelectric layer is not damaged by a reducing atmosphere generated during the process of forming the ferroelectric memory element, and a method for manufacturing the same.